The FBI has released a study of Active Shooter incidents in the United States between 2000 and 2013.

Introduction
In 2013, the president signed into law the Investigative Assistance for Violent Crimes Act of 2012, which granted the attorney general the authority to assist in the investigation of “violent acts and shootings occurring in a place of public use” and in the investigation of “mass killings and attempted mass killings at the request of an appropriate law enforcement official of a state or political subdivision.”

To provide further clarity on these threats, the Federal Bureau of Investigation (FBI) in 2014 initiated a study of “active shooter” incidents. The goal of the FBI study is to provide federal, state, and local law enforcement with data so they can better understand how to prevent, prepare for, respond to, and recover from these incidents.

Active shooter is a term used by law enforcement to describe a situation in which a shooting is in progress and an aspect of the crime may affect the protocols used in responding to and reacting at the scene of the incident. Unlike a defined crime, such as a murder or mass killing, the active aspect inherently implies that both law enforcement personnel and citizens have the potential to affect the outcome of the event based upon their responses.